Heretofore an antitheft device for an audio device is known, in which a microcomputer is used for the antitheft purpose, in the memory of which an identification number is stored; the identification number should be inputted in order to use the audio device; and various functions of the audio device can work, only when an inputted code is in accordance with the stored identification number. That is, even if somebody steals the audio device, unless he knows the identification number, he cannot operate the audio device and therefore the device has an antitheft effect.
An antitheft device for an audio device for use on vehicle has been disclosed in Japanese patent application No. Sho-60-104434. This device has an inconvenience that a code representing the identification number must be inputted necessarily before use.
Further this device has a drawback that if its power supply feeding the microcomputer with electric power is switched off, no identification number can be identified, because the content of its memory is not held.